1. Field of the Invention
The present invention relates to the use of an integrated circuit micromodule as a surface-mounted package on a substrate of interconnections.
Surface-mounting combines a set of operations for the placing of miniature components on the surface of a printed circuit or a silk-screen printed substrate of a hybrid circuit.
The components are placed by automatic positioning machines on the substrate and then soldered. They are not provided with outgoing wires and do not require holes in the circuit in order to be attached. Their packaging is done in alveolar strips or in tubes. They are drawn out by suction in order to be then transferred to the substrate.
The term "micromodule" refers to the miniature unit formed chiefly by one or more integrated circuit chips and a connector formed by fine and substantially plane contact zones, this miniature unit being designed to be inserted into a thin information carrier of the chip card or memory-based key type so that the connector is flush with the surface of the information carrier, the chip being embedded in the carrier. The connector has six to eight contact zones distributed in two rows that provide for five to eight standardized ports or points of access to the chip: the electrical ground GND, the logic supply VCC, the programming voltage VPP (not always used), zero reset RST, clock CLK and series data input/output I/O, two other zones being available for specific or future applications (8-contact connector). International standards define the various characteristics of the micromodules (ISO 7810 to 7816). One of these characteristics is their small thickness. Indeed, a micromodule typically has a thickness of less than 0.6 millimeters.
2. Discussion of the Related Art
Various industrial methods for the manufacture of micromodules have been developed. A first known method consists chiefly in attaching a chip to a metal strip that bears the contact zones which are mechanically partitioned. The chip is connected by wires soldered to the different contact zones. The chip and the wires are then coated with a drop of protective resin. A strip of micromodules in series is obtained. A partitioning operation then gives the individual micromodules which will then be fitted into cards.
To resolve the problems of adhesion of the resin on the metallized gate and of the overflow of resin on the contact zones of the connector, it is preferred to use molded dielectric or dielectric transferred under heat to the grid so as to form a single-face metallized carrier on which the chip is mounted on the dielectric side and connected by wires going through perforations of the dielectric and soldered to the contact zones.
Another known method for making a single-face metallized carrier for micromodules uses a perforated dielectric strip, on one face of which metal is laminated. The metal is then etched to form the contact zones of the connector.
Other methods finally use a dual-faced metallized supporting film, with one face for the connection to the chip and the other face forming the connector. In one improvement, there is designed a metal or dielectric enclosure that surrounds the chip and its connections. This enclosure is filled with protective resin (silicone type thermohardening resin or polyurethane type thermoplastic resin). A micromodule with perfectly reproducible and controlled dimensions and shape is obtained. The protective enclosure filled with resin efficiently protects the chip and its connections from chemical corrosion and mechanical stresses. A micromodule such as this and a corresponding method is described, for example, in the European patent application published under number 0 391 790 filed on Apr. 3, 1990 under number 90 400909.
These micromodules have been developed chiefly for so-called secured applications: disposable or rechargeable prepaid cards, access checking, subscriber cards, bank cards, pay television cards, single service or multiple service cards, etc. For these applications of the micromodules, integrated circuit chips have been specially developed. These chips integrate different protective systems and meet the specifications of a standardized type of connection. In simple memory chips, protective systems are provided in the form of wired logic. Fuses are used to prevent write access to certain zones of the memory. A bearer code for the user of the card may be provided to permit read/write access to the memory zones and to deactivate the chip if a wrong carrier code is presented (in the case of stolen cards). An issuing party code from the organization that delivers the card to the user may be contained in the chip to deactivate it if the code is wrong (in the case of false cards).
In microprocessor-based chips, protection systems of greater sophistication may be used, for example with the implementation of cryptographic algorithms to secure data transfers, the methodical use of bearer and issuing party codes, the possibility of rehabilitating a card (by the releasing of a deactivated chip) etc.
There is a system of software operation that further enables the dynamic management of the memory or the loading of specific programs when the card is customized.
All these secured chips furthermore have security sensors that check the operational conditions of use of the card: whether the frequency of the clock signal CLK is too low or the logic supply voltage Vcc is too high, the presence of the final passivation layer of the chip, etc.
Each of the sensors delivers a binary information element that is used directly to activate a physical security mechanism (deactivation) or is stored to be used by a program for the management of anomalies.
The chip is deactivated, for example, by forcing the level of the resetting signal (RST) to zero or by blocking access to strategic information elements.
The standardized technology of micromodules has therefore led to the development of integrated circuit chips with five to eight outputs that are highly secured in terms of both hardware and software. This has provided for the growth that has been seen in the use of micromodule-based cards.
The development of numerous electronic applications for data processing or telematics requires, as a prerequisite condition, the securing of the ports and of the transfers of data elements. To this end, chip-based readers have been integrated with microcomputers and customized memory-based key readers have been planned in decoders of encrypted systems. In the invention, it is sought to resolve this problem of security, within electronic or computer equipment other than chip cards, on printed circuit cards or silk-screen printed substrates.
One possible idea might have been to use a secured chip developed for micromodules as a standard electronic component by placing it in a standardized package of semiconductors, for example a DIL or SO package.
However, it has been seen that these chips use five to eight outputs. Furthermore, the chips of the most complex micromodules take up a large area. These chips therefore require wide DIL or SO packages with at least 8 to 16 outlets.
Now, the growing complexity of electronic applications requires an increasingly intensive degree of miniaturization especially in fields related to on-board installations or installations in homes or individual premises. It is necessary to propose equipment that is both efficient and compact. Under these conditions, the addition of one or more packages with 8 to 16 outputs on a printed circuit may prove to be difficult for some of these applications.